Spark plug having a mica insulator for internal combustion engines



Nov. 17, 1942. E. ZANZI 2,301,990

SPARK PLUG HAVING A MICA INSULATOR FOR INTERNAL COMBUSTION ENGINES Filed001.. 29, 1940 Fi .1 r Fig.2

Patented Nov. 17; 1942 UNITED STATES PATENT OFFICE SPARK PLUG HAVING AMICA INSULATOR FOR. INTERNAL COMBUSTION ENGINES Enrico Zanzi, Ivrea,Italy; vested in the Alien Property Custodian Application October 29,1940, Serial No. 363,374 In Italy November 21, 1939 1 Claim.

This invention relates to improvements in spark plugs having a micainsulator. for internal combustion engines. The insulator is generallycon- 1 stituted by mica rings fitted on the core and tightly pressed. Inspite of the high pressure the current may pass through the capillaryinterstices between adjacent rings. These rings, in the knownconstructions, are separated from the metallic core by means of a mica.tube, which constitutes a screen preventing leaks of -15,000 v. 10

current in a radial direction from the core towards the spark plug bodythrough the rings. Current leaks, however, may occur from the core headto the spark plug body first in an axial direction through the gapbetween the central mica tube and the ring pack and then in a radialdirection through the ring pack.

According to this invention the mica rings are also fitted on a centralmica tube coating the core and, moreover, the ring pack is introducedinto a mica tube covering the inner wall of the spark plug body; thecurrent accidentally flowing from the core head may pass through thecentral tube and ring pack and then between the rings but cannot reachdirectly the spark plug body; it

flows to the base of the body passing through a gap between the ringpack and the outer mica tube.

The resistance to the current flow through interstices between mica andmica is thus increased .to nearly twice the former resistance.

According to this invention and in view of the fact that the rings,which are in closer proximity to the-electrodes are more exposed to bedamaged by the current, are subdivided into two concentric ringsseparated by a wide gap, so that when one 01' these rings is damaged,the dispersion current is lead on two paths along the axis or the firstundivided ring between the core head and the base of the sparkplug-body.

The annexed drawing shows an embodiment of the invention.

Fig. l is an axial section of a spark plug of ordinary construction,

Fig. 2 is an axial section or a sparkplug or a similar type but improvedaccording to this invention.

Spark plugs are constituted (Fig. 1) by a body I connected to the enginemass and a core 2 connected to the source 01. power; the'body and core 5are insulated from each other.

A mica insulator is preferably used for spark plugs exposed to hightemperatures owing to its strength and is generally constituted by apack oi mica rings 3 Fig.

1) fitted on the core and pressed against the head to with theinterposition of a mica tube 4 I and in many cases also of a copper tube5. be-

, tween the mica tube and core. An annularchamber 1 between the ringpack 3 and body I .forms an extension of the chamber 6 of the sparkplug.

Although the mica rings are highly pressed together, a dispersion of10-1500 v. current may occur through the capillary interstices; the tube4 prevents a direct dispersion from the core 2; the current may onlyflow from the head 2a through the narrow gap between the tube 4 and pack3 and reaches the wall of the body I through the annular chamber 1, inwhichcarbonaceous deposits may be collected.

According to this invention the annular cham-.

her I is eliminated and the ring pack 3 fitted, as in the former case,on the core 2 with the interposition of a mica tube 4 and a copper tubeI follows a path twice as long as the path in the ordinary construction.

According to a further improvement, the ring pack 3 is provided on theside or the chamber 6 with a wide and deep circular slot ll forming anextension of the chamber 8 and obtained by subdividing, along a sectionof the pack, each ring into two concentric rings 3a and lb; the rings 3abear on the head 2a of the core and the rings 3b on the shoulder la ofthe body or the spark plug. The current escaping between the head 2a andshoulder la must thus follow a path equal at least to twice the depth ofthe slot II.

The spark plug may be disassemblable or notand I be provided withsparking points or any'shape' and, generally, various changes may bemade in the details of construction without departing from the limits ofthe invention.

What I claim is:

A spark plug for internal combustion enginu, 7

comprising a core of conducting material, amica tube fitted on saidcore, a pack or'mica rings surrounding said mica tube and having on thespark side a wide and deep slot,

a secondmicatubeinwhichsaidpackotmicaringsisintroducedandacasingotconducting material surrounding said secondmica tube.

ENRIOOZANZI,

